1. Field of the Invention
The present invention relates to serial bus management. In particular, the present invention relates to a method and apparatus for preventing loops in a serial bus system.
2. The Prior Art
Modern electronic equipment has greatly enhanced the quality of our lives. However, as the use of such equipment has increased, so has the need to connect equipment purchased from different manufacturers. For example, while a computer and a digital camera may each be useful when used alone, the ability to connect the digital camera to the computer and exchange information between the two makes the combination even more useful. Therefore, a need was apparent for a serial bus standard that would allow for the connection and communication between such devices.
The IEEE 1394-1995 standard was developed to satisfy this need. This standard, revolutionized the consumer electronics industry by providing a serial bus management system that featured high speeds and the ability to xe2x80x9chotxe2x80x9d connect equipment to the bus; that is, the ability to connect equipment without first turning off the existing connected equipment. Since its adoption, the IEEE 1394-1995 standard has begun to see acceptance in the marketplace with many major electronics and computer manufacturers providing IEEE 1394-1995 connections on equipment that they sell.
However, as technologies improved, the need to update the IEEE 1394-1995 standard became apparent. Improvements such as higher speeds and longer connection paths are needed. There is currently an improved standard in development, herein referred to as the P1394b, which will provide such improvements.
One problem that is associated with serial bus systems is that of loops occurring in a system. In order for a serial bus system to function properly, one end of the bus cannot be connected to the other. Loops typically occur when a end user, typically a consumer, inadvertently connects a new device to the bus in such a manner that a loop is formed. If this occurs, a xe2x80x9cloopxe2x80x9d is formed in the system, and the system will fail to properly initialize. Once a loop is formed, the system will not function properly, since communications between devices is impossible.
Consequentially, there is a need for an method for managing a serial bus system that detects when a loop has been formed, and eliminates the loop.
Furthermore, since there will be equipment utilizing both the xcex1 and xcex2 standards on the market, there is a need for a serial bus loop-breaking system that is compatible with the xcex2 standard, and is backwards-compatible with the xcex1 standard.
Finally there is a need for a system that prevents the above problems by building a loop-free connection from the start.
The invention satisfies the above needs. The present invention relates to a method and apparatus for preventing loops in a full-duplex bus. A preferred method for preventing loops in a full-duplex bus has the following acts: selecting at least two candidates to join the bus; establishing a dominant candidate from one of the at least two candidates; testing for loops in the bus; and joining the dominant candidate if no loops are found in the bus.
Another preferred method for preventing loops in a full-duplex bus has the following acts: selecting a plurality candidates to join the bus: establishing at least one dominant candidate; testing for loops in the bus; and joining the at least one dominant candidate if no loops are found in the bus.
Another preferred method for breaking loops in a bus containing both full-duplex and uniplex devices is disclosed, the method comprising the acts of: determining whether the loop comprises only full-duplex devices and breaking the loop at any point on the bus; determining whether the loop comprises only uniplex devices and quarantining the loops comprising uniplex devices from the bus; and determining whether the loop comprises both uniplex and full-duplex devices, and breaking the loop by utilizing only full-duplex device to break the loop.
An electronic device adapted to communicate on a full-duplex bus is disclosed, the device comprising: means for selecting two candidates to join the bus; means for establishing a dominant candidate; means for testing for loops in the bus; and means for joining the dominant candidate if no loops are found in the bus.
An electronic device adapted to communicate on a full-duplex bus is disclosed, the device comprising: means for selecting a plurality candidates to join the bus; means for establishing at least one dominant candidate; means for testing for loops in the bus; and means for joining the at least one dominant candidate if no loops are found in the bus.
A method for detecting and breaking loops in a full-duplex electronic bus is disclosed, the method comprising the acts of: selecting candidates to join to the bus; arbitrating for control of the bus; transmitting a loop test packet containing a unique identifier on the bus; receiving loop test packets from the bus, the received loop test packets containing a unique identifier; surrendering control of the bus if any the unique identifier contained in any the received loop test packet is greater than the unique identifier contained in the transmitted loop test packet and waiting for the bus to return to idle before attempting to join the bus again; and joining the selected candidates to the bus if any the unique identifier contained in the transmitted loop test packet is greater than or equal to any the unique identifier contained in the received loop test packet.
A method for detecting and breaking loops in a full-duplex electronic bus, the method comprising the acts of: connecting a device to the bus; testing for a loop in the bus; quarantining the device from the bus a loop is found; resuming the device if no loop is found; testing for a loop in the bus if the device does not resume within a predetermined time period; activating the device; and testing for a loop in the bus if the device does not activate within the predetermined time period.
Finally, a program storage device readable by a machine, tangibly embodying a program of instructions executable by a machine to prevent loops on a full-duplex bus, is disclosed, the device comprising: means for selecting a plurality candidates to join the bus; means for establishing at least one dominant candidate; means for testing for loops in the bus; and means for joining the at least one dominant candidate if no loops are found in the bus.